add way to debug generated BPF code (iovisor#1494)

tools/tcpretrans.py

@@ -1,10 +1,10 @@
 #!/usr/bin/python
 # @lint-avoid-python-3-compatibility-imports
 #
-# tcpretrans Trace TCP retransmits and TLPs.
+# tcpretrans Trace or count TCP retransmits and TLPs.
 # For Linux, uses BCC, eBPF. Embedded C.
 #
-# USAGE: tcpretrans [-h] [-l]
+# USAGE: tcpretrans [-c] [-h] [-l]
 #
 # This uses dynamic tracing of kernel functions, and will need to be updated
 # to match kernel changes.
@@ -38,6 +38,7 @@
 parser.add_argument("-c", "--count", action="store_true",
  help="count occurred retransmits per flow")
 args = parser.parse_args()
+debug = 0
 
 # define BPF program
 bpf_text = """
@@ -188,6 +189,9 @@
  bpf_text = bpf_text.replace("IPV4_CORE", "ipv4_events.perf_submit(ctx, &data4, sizeof(data4));")
  bpf_text = bpf_text.replace("IPV6_CORE", "ipv6_events.perf_submit(ctx, &data6, sizeof(data6));")
 
+if debug:
+ print(bpf_text)
+
 # event data
 class Data_ipv4(ct.Structure):
  _fields_ = [